1. Field of the Invention
The invention relates to a new process for the production of tetronic acid alkyl esters, and to a new process for producing tetronic acid for such esters.
2. Background Art
Tetronic acid alkyl esters are known compounds, which can be used as valuable intermediate products, e.g., for pharmaceutical agents. See for this purpose, e.g., Pelter et al., J. Chem. Soc. Perkin Trans. I, (1987), p. 717 ff., or Pelter et al., Tetrahedron Letters, No. 18, (1979), p. 1627 ff.
Production of tetronic acid methyl ester is known, e.g., from West German PS 2,845,037, in which a 4-bromo-3-methoxybut-2-ene carboxylic acid lower alkyl ester is cyclized in an organic solvent with a Lewis acid, e.g., zinc dibromide. Yields between 70 and 80 percent are described. But from an ecological viewpoint, it is a disadvantage that heavy metal catalysts, which cannot be recycled, must be used in such process. The reworking of the process with the appropriate 4-chlorine analog, moreover, has shown that the yield, significantly lower than indicated, must be estimated at about 50 percent.